Anyway, I have a lot of smoke stain coming from my water heater exhaust grille. No, there's no critters in the burner tube (or whatever it's called). Been there, done that, tossed the carcass. Have the seemingly permanent smoke stain from THAT fire.

This stain is from this past weekend when I had the water heater on for three days. It actually looks like it can rub off (but I hesitate to do that without water, and right now it's at a storage unit).

It’s not smoking now because whatever was in there burned up. Looks like things got very hot! After you open it up I would be interested to see inside! WW has a good point. I would definitely find out what caused it before I used it again!